1. Technical Field
Embodiments disclosed herein relate to the field of optical devices for spectroscopic measurements of a fluid. In particular, embodiments disclosed herein relate to agile light sources for spectroscopic measurements of fluids.
2. Description of Related Art
In the field of oil exploration and extraction there is often the need to perform measurements of samples to determine their chemical composition. In many cases, methods and systems to perform optical measurements use a light source to provide an input light to the sample. Methods and systems to perform optical measurements include filters and other spectrally resolved optical devices that are typically complicated to manufacture, involving time-consuming procedures. State-of-the-art optical measurement techniques are difficult to apply in hydrocarbon exploration and extraction due to the wide spectral range involved in the measurement, covering from the ultra-violet (UV, 250 nm-450 nm), the visible (VIS, 450 nm-750 nm) and near infrared (NIR, 750 nm-2500 nm) to the mid-infrared and beyond (2500 nm-10 μm). Some prior art approaches attempt to overcome the broad band problem by having a plurality of manufactured filters and spectrally resolved optical devices mounted onto a rotating wheel. This approach has the drawback of increasing device overhead in a limited space environment such as the downhole environment, in an oil exploration and extraction application. Furthermore, with filter rotation and fluid flow in an optical cell (e.g., for fluid samples), the measurement system becomes difficult to align and prone to errors. Prior art devices are mechanically and electronically complex systems due to the need for wheel synchronization and mechanical robustness introduced by the rotating filter wheel mechanism. Prior art devices have another drawback in that input light passes through the filters at different times. This adds complexity to data analysis, especially when flow is inhomogeneous, compromising accuracy of results due to undesirable latency caused by the slow rotation of typical filter wheels, and rotation jitter.
Another drawback of conventional filters and other spectrally resolved optical devices is manufacturability. Indeed, filters with spectral profiles may be highly costly to fabricate within a desirable error tolerance. Typically, a desired model is provided to a manufacturer for thin film deposition. During deposition, a real time optimization re-adjusts thicknesses of remaining film layers when a film thickness deviates from a desired value. After filters and spectrally resolved optical devices are manufactured, a calibration process is typically needed to characterize the response of the optical measurement system for samples at different temperatures and pressures. Thus, manufacturing steps in state of the art optical measurement systems introduce error and high cost to the system.
What is needed are methods and systems to allow spectral measurements of samples using a broad spectral band with a reduced number of physical components. Also needed are systems that are rugged and compact, providing detailed information about sample composition, and methods for using the systems.
Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements.